Adaptive antenna transmitting/receiving apparatus

ABSTRACT

Reception quality measuring circuit ( 107 ) measures the reception quality of received data delivered from adder ( 103 ). When the reception quality measured by reception quality measuring circuit ( 107 ) is less than a certain threshold value, transmission antenna weight control circuit ( 108 ) applies multipliers ( 106   1   –196   N ) with stored transmission antenna weights, that is, transmission antenna weight W″ stored therein when the reception quality exceeded the threshold value at the last time, instead of transmission antenna weights W′ generated by antenna weight converting circuit ( 105 ).

TECHNICAL FIELD

The present invention relates to an adaptive antennatransmitting/receiving apparatus which is a transmitting/receivingapparatus using an adaptive antenna, and more particularly, to anadaptive antenna transmitting/receiving apparatus which generatestransmission antenna weights based on reception antenna weights.

BACKGROUND ART

Generally, in mobile transmission systems, interference from otherusers, i.e., multi-user interference is a significant factor to limitthe system capacity. Thus, for increasing the system capacity, anadaptive antenna technique is considered effective since it suppresses areceived signal in a particular direction (interfering wave direction)during reception, and avoids interference in unnecessary directionsduring transmission.

FIG. 1 illustrates a prior art example of a transmitting/receivingapparatus using such an adaptive antenna (adaptive antennatransmitting/receiving apparatus). As illustrated in FIG. 1, thisconventional adaptive antenna transmitting/receiving apparatus comprisesN antenna elements 101 ₁–101 _(N). N multipliers 102 ₁–102 _(N), adder103, reception antenna weight generating circuit 104, antenna weightconverting circuit 105, and N multipliers 106 ₁–106 _(N).

Multipliers 102 ₁–102 _(N) perform weighted multiplications bymultiplying received signals from antenna elements 101 ₁–101 _(N) byreception antenna weights W=(w₁, w₂, . . . , w_(N)) generated byreception antenna weight generating circuit 104, respectively. Adder 103adds together the received signals of the respective antennas weightedby multipliers 102 ₁–102 _(N) to deliver as single received data.

Reception antenna weight generating circuit 104 is applied with thereceived data delivered from adder 103, and generates weightingcoefficients which permit the received data to have an optimal value asreception antenna weights W.

The operation of reception antenna weight generating circuit 104 isgenerally implemented by MMSE (minimum Mean Squared Error) control whichadaptively updates weighting coefficients to minimize a mean squarederror of weighted and added received signals and a reference signal.Known algorithms for realizing MMSE include LMS (Least Mean Square) andRLS (Recursive Least Square) algorithms, and the like. In the presentinvention, no limitations are particularly imposed to the algorithm usedin reception antenna weight generating circuit 104.

Reception antenna weights W=(w₁, w₂, . . . , w_(N)) generated byreception antenna weight generating circuit 104 are used for weightingreceived signals in multipliers 102 ₁–102 _(N), and are also applied toantenna weight converting circuit 105.

Antenna weight converting circuit 105 converts reception antenna weightsW generated by reception antenna weight generating circuit 104 totransmission antenna weights W′=(w′₁, w′₂, . . . , w′_(N)). Thisconversion is performed for correcting an amplitude/phase deviationamong branches of an RF transmitting circuit, or for correcting afrequency difference of transmission/reception whentransmission/reception are different in frequency as an FDD (FrequencyDivision Duplex) system, and is basically performed with the intentionto generate transmission weights W′ for forming a similar pattern to adirectivity pattern formed in the reception.

Multipliers 106 ₁–106 _(N) multiply data to be transmitted bytransmission antenna weights W′ delivered from antenna weight convertingcircuit 105, respectively.

In the conventional adaptive antenna transmitting/receiving apparatusillustrated in FIG. 1, a plurality of N antenna elements 101 ₁–101 _(N)are arranged in an array, and weighting coefficients of respectiveantenna elements 101 ₁–101 _(N) are adaptively controlled through signalprocessing to conduct a control for increasing an antenna gain(directivity) in a particular direction. On the other hand, intransmission, the reception antenna weights are calibrated to generatetransmission antenna weights which are multiplied by signals to betransmitted of respective users, such that the resulting signal aretransmitted to have the directivity in a desired wave user direction andto reduce interference given to other user directions. An adaptiveantenna transmitting/receiving apparatus in such a configuration isdescribed in literature [1] listed below.

Literature [2] listed below shows a system for controlling receptionantenna weights so as to minimize a mean squared error after RAKEcombination generated using a despread pilot symbol and a determinationinformation data symbol as reference signals, for example, as a methodof calculating optimal reception weights.

Also, literature [3] listed below describes a method of usingtransmission antenna weights which are generated based on antennaweights generated as described above, as a method of generatingtransmission antenna weights.

[1] NTT DoCoMo Technical Journal, Vol. 8, No. 1 (April 2000);

[2] S. Tanaka, M. Sawahashi and F. Adachi, “Pilot symbol-assisteddecision-directed coherent adaptive array diversity for DS-CDMA mobileradio reverse link”, IEICE Trans. Fundamentals, Vol. E80-A, pp.2445–2454, (December, 1997); and

[3] Tanaka, Harada, Ihara, Sawahashi and Adachi, “Outdoor experimentcharacteristics of adaptive antenna array diversity reception in W-CDMA,Technical Report RCS99–127, pp. 45–50 (October 1999).

In the conventional adaptive antenna transmitting/receiving apparatusillustrated in FIG. 1, the transmission antenna weights are generatedbased on the reception antenna weights generated for reception. This isintended to apply the directivity pattern formed during reception, as itis, to transmission. However, if the apparatus fails to generate optimalantenna weights, for example:

(1) when the generation of reception antenna weights is in course ofconvergence, so that optimal weights have not been formed;

(2) when the reception line quality is so bad that the generation ofoptimal reception antenna weights encounters difficulties;

(3) when the reception line is instantaneously interrupted due toshadowing or the like;

(4) when a failure in the apparatus or the like results in defectivereception, and the like,

the transmission antenna weights are not either optimized. For thisreason, it is contemplated that not only the directivity is not formedfor a desired station, but also larger interference is given to otherusers by contraries, resulting in a significant degradation of thetransmission characteristic as well as the reception characteristic.

Conventional techniques for controlling transmission antenna weights tohave optimal values are described in JP-2000-22611-A, JP-2001-217759-A,and the like.

JP-2000-22611-A describes an adaptive antenna transmitting/receivingapparatus which comprises an incoming direction estimating circuit, andestimates an incoming direction by the incoming direction estimatingcircuit to correct transmission antenna weights. However, thisconventional adaptive antenna transmitting/receiving apparatus cannotestimate an incoming direction if the reception line quality isdegraded, resulting in the inability to control optimal transmissionweights, and possible erroneous control conducted in some cases tosignificantly degrade the transmission characteristic.

JP-2001-217759-A in turn describes an adaptive antennatransmitting/receiving apparatus which controls transmission antennaweights based on an interference degree calculated by an interferencedegree calculating unit. However, this conventional adaptive antennatransmitting/receiving apparatus is similar in that it cannot calculatethe interference degree itself if the reception line quality isdegraded, resulting in the inability to control optimal transmissionweights, and possible erroneous control conducted in some cases tosignificantly degrade the transmission characteristic.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an adaptive antennatransmitting/receiving apparatus which is capable of preventing thetransmission characteristic from significantly degrading when optimalreception antenna weights cannot be generated.

To achieve the above object, an adaptive antenna transmitting/receivingapparatus of the present invention comprises:

a plurality of antenna elements;

a plurality of first multipliers for performing a weightedmultiplication by multiplying received signals from the plurality ofantenna elements by reception antenna weights, respectively;

an adder for adding together the received signals of the respectiveantennas weighted by the plurality of first multipliers to deliver assingle received data;

a reception quality measuring circuit for measuring a reception qualityof the received data delivered from the adder;

reception antenna weight generating circuit applied with the receiveddata delivered from the adder for generating weighting coefficientswhich permit the received data to have an optimal value, as thereception antenna weights;

an antenna weight converting circuit for converting the receptionantenna weights generated by the reception antenna weight generatingcircuit into transmission antenna weights;

a transmission antenna weight control circuit for delivering thetransmission antenna weights delivered from the antenna weightconverting circuit and stored therein the delivered transmission antennaweights when the reception quality measured by the reception qualitymeasuring circuit exceeds a previously set threshold value, and fordelivering the stored transmission antenna weights instead of thetransmission antenna weights delivered from the antenna weightconverting circuit when the reception quality is less than the thresholdvalue; and

a plurality of second multipliers for multiplying data to be transmittedby the transmission antenna weights delivered from the transmissionantenna weight control circuit, respectively.

According to the present invention, the reception quality circuitmeasures the reception quality of received data, and the transmissionantenna weight control circuit does not use the transmission antennaweights generated by the antenna weight converting circuit as they are,but uses stored transmission antenna weights, i.e., the transmissionantenna weights when the reception quality exceeded the threshold valueat the last time, when the reception quality is less than the previouslyset threshold value, thus making it possible to prevent the antennaelements from being controlled with erroneous transmission antennaweights to significantly degrade the transmission characteristic.

Also, another adaptive antenna transmitting/receiving apparatus of thepresent invention further comprises a reception quality measuringcircuit for measuring the reception quality of received data deliveredfrom the adder, and a transmission antenna weight control circuit,wherein the transmission antenna weight control circuit delivers thetransmission antenna weights delivered from the antenna weightconverting circuit, as they are, when the reception quality measured bythe reception quality measuring circuit exceeds the previously setthreshold value, and delivers previously set values instead of thetransmission antenna weights delivered from the antenna weightconverting circuit, as the transmission antenna weights, when thereception quality is less than the threshold value.

According to the present invention, the reception quality circuitmeasures the reception quality of received data, and the transmissionantenna weight control circuit does not use the transmission antennaweights generated by the antenna weight converting circuit as they are,but uses the previously set values as the transmission antennas, whenthe reception quality is less than the previously set threshold value,thus making it possible to prevent the antenna elements from beingcontrolled with erroneous transmission antenna weights to significantlydegrade the transmission characteristic.

Also, the transmission antenna weight control circuit may deliver thepreviously set values which have a value only for a weight correspondingto a particular antenna element and zero for all the remaining weightscorresponding to the other antenna elements, as the transmission antennaweights.

Further, the reception quality measuring circuit may measure thereception quality based on any of a signal-to-noise power ratio, a biterror rate, and a block error rate of the received data which is theoutput of the adder circuit.

It is an object of the present invention to provide an adaptive antennatransmitting/receiving apparatus which is capable of preventing thetransmission characteristic from significantly degrading when optimalreception antenna weights cannot be generated.

To achieve the above object, an adaptive antenna transmitting/receivingapparatus of the present invention comprises:

a plurality of antenna elements;

a plurality of first multipliers for performing a weightedmultiplication by multiplying received signals from the plurality ofantenna elements by reception antenna weights, respectively;

an adder for adding together the received signals of the respectiveantennas weighted by the plurality of first multipliers to deliver assingle received data;

a reception quality measuring circuit for measuring a reception qualityof the received data delivered from the adder;

reception antenna weight generating circuit applied with the receiveddata delivered from the adder for generating weighting coefficientswhich permit the received data to have an optimal value, as thereception antenna weights;

an antenna weight converting circuit for converting the receptionantenna weights generated by the reception antenna weight generatingcircuit into transmission antenna weights;

a transmission antenna weight control circuit for delivering thetransmission antenna weights delivered from the antenna weightconverting circuit and stored therein the delivered transmission antennaweights when the reception quality measured by the reception qualitymeasuring circuit exceeds a previously set threshold value, and fordelivering the stored transmission antenna weights instead of thetransmission antenna weights delivered from the antenna weightconverting circuit when the reception quality is less than the thresholdvalue; and

a plurality of second multipliers for multiplying data to be transmittedby the transmission antenna weights delivered from the transmissionantenna weight control circuit, respectively.

According to the present invention, the reception quality circuitmeasures the reception quality of received data, and the transmissionantenna weight control circuit does not use the transmission antennaweights generated by the antenna weight converting circuit as they are,but uses stored transmission antenna weights, i.e., the transmissionantenna weights when the reception quality exceeded the threshold valueat the last time, when the reception quality is less than the previouslyset threshold value, thus making it possible to prevent the antennaelements from being controlled with erroneous transmission antennaweights to significantly degrade the transmission characteristic.

Also, another adaptive antenna transmitting/receiving apparatus of thepresent invention further comprises a reception quality measuringcircuit for measuring the reception quality of received data deliveredfrom the adder, and a transmission antenna weight control circuit,wherein the transmission antenna weight control circuit delivers thetransmission antenna weights delivered from the antenna weightconverting circuit, as they are, when the reception quality measured bythe reception quality measuring circuit exceeds the previously setthreshold value, and delivers previously set values instead of thetransmission antenna weights delivered from the antenna weightconverting circuit, as the transmission antenna weights, when thereception quality is less than the threshold value.

According to the present invention, the reception quality circuitmeasures the reception quality of received data, and the transmissionantenna weight control circuit does not use the transmission antennaweights generated by the antenna weight converting circuit as they are,but uses the previously set values as the transmission antennas, whenthe reception quality is less than the previously set threshold value,thus making it possible to prevent the antenna elements from beingcontrolled with erroneous transmission antenna weights to significantlydegrade the transmission characteristic.

Also, the transmission antenna weight control circuit may deliver thepreviously set values which has a value only for a weight correspondingto a particular antenna element and zero for all the remaining weightscorresponding to the other antenna elements, as the transmission antennaweights.

Further, the reception quality measuring circuit may measures thereception quality based on any of signal-to-noise power ratio, a biterror rate, and a block error rate of the received data which is theoutput of the adder circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of aconventional adaptive antenna transmitting/receiving apparatus; and

FIG. 2 is a block diagram illustrating the configuration of an adaptiveantenna transmitting/receiving apparatus according to one embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, one embodiment of the present invention will be described indetail with reference to the drawings.

FIG. 2 is a block diagram illustrating the configuration of an adaptiveantenna transmitting/receiving apparatus according to one embodiment ofthe present invention. In FIG. 2, components identical to the componentsin FIG. 1 are designated the same reference numerals, and descriptionthereon is omitted.

The adaptive antenna transmitting/receiving apparatus of this embodimentadditionally comprises reception quality measuring circuit 107, andtransmission antenna weight control circuit 108, added to theconventional adaptive antenna transmitting/receiving apparatusillustrated in FIG. 1.

In the adaptive antenna transmitting/receiving apparatus of thisembodiment, since transmission antenna weight control circuit 108 isprovided between antenna weight converting circuit 105 and multipliers106 ₁–106 _(N), multipliers 106 ₁–106 _(N) in this embodiment do notmultiply data to be transmitted by transmission antenna weights W′delivered from antenna weight converting circuit 105, but multiply thedata to be transmitted by transmission antenna weight W″ delivered fromtransmission antenna weight control circuit 108.

This embodiment is characterized in that reception quality measuringcircuit 107 and transmission antenna weight control circuit 108 areprovided in an adaptive antenna transmitting/receiving apparatus forgenerating transmission antenna weights based on reception antennaweights.

Reception quality measuring circuit 107 measures the reception qualityof received data delivered from adder 103 by calculating SIR(Signal-to-Noise power Ratio), BER (Bit Error Rate), BLER (BLock ErrorRate), or the like for notification to transmission antenna weightcontrol circuit 108.

Transmission antenna weight control circuit 108 is applied withtransmission antenna weights W′ which are the outputs of antenna weightconverting circuit 105, and the reception quality which is the output ofreception quality measuring circuit 107 for determining transmissionantenna weights W″. Specifically, transmission antenna weight controlcircuit 108 determines whether or not transmission antenna weights W′converted by antenna weight converting circuit 105 are actually used.The criterion for the determination used herein is the reception qualitymeasured by reception quality measuring circuit 107.

Transmission antenna weight control circuit 108 delivers transmissionantenna weights W′ from antenna weight converting circuit 105, as theyare, to multipliers 106 ₁–106 ₂, when the reception quality measured byreception quality measuring circuit 107 exceeds a previously setthreshold value.

Then, transmission antenna weight control circuit 108 conducts a controlsuch that the transmission antenna weights, which are the outputs ofantenna weight converting circuit 105, are not used as they are, whenthe reception quality is less than the threshold value.

As an example of this control, previously calculated antenna weights maybe continuously used as they are, for example, when the receptionquality is less than a certain threshold value, such that thetransmission antenna weights are not updated. In this event,transmission antenna weight control circuit 108 compares the receptionquality, which is the output of reception quality measuring circuit 108,with a previously set threshold value, and delivers the transmissionantenna weights, which are the outputs of antenna weight convertingcircuit 105, to multipliers 106 ₁–106 _(N) as they are, when thereception quality exceeds the threshold value, and stores therein thedelivered transmission antenna weights. Then, when the reception qualityis less than the threshold value, transmission antenna weight controlcircuit 108 delivers the stored transmission antenna weights (thetransmission antenna weight when the reception quality exceeded thethreshold value at the last time) instead of the transmission antennaweights which are the outputs of antenna weight converting circuit 105.

In this way, an erroneous detection in an incoming direction due to adegradation in reception characteristic can be prevented from affectingthe transmission antenna weights.

Alternatively, transmission antenna weight control circuit 108 maydeliver previously set values to multipliers 106 ₁–106 _(N) astransmission antenna weights W″ instead of transmission antenna weightsW′ delivered from antenna weight converting circuit 105 when thereception quality measured by reception quality measuring circuit 107 isless than a previously defined threshold value.

The previously set values are, for example, W″=(1,0, . . . ,0), i.e.,weighting coefficients having a value only for a weight corresponding toa particular antenna element, and zero for the others, such asw₁=(1.0,0.0), w₂–w_(N)=(0.0,0.0).

Such a control, if conducted, will lose a directivity gain duringtransmission which has been provided when reception antenna weightgenerating circuit 104 is correctly estimating an incoming direction,but can avoid reception antenna weight generating circuit 104 frommaking an error in estimating an incoming direction to cause a danger oferroneously forming the directivity to other than a desired station upontransmission, and giving interference to other users. Also, when aninstantaneous interruption extends for a long time to cause a largechange in incoming direction, it is possible to prevent a degradation incharacteristic, on the contrary, because the transmission directivitycannot follow.

1. An adaptive antenna transmitting/receiving apparatus comprising: aplurality of antenna elements; a plurality of first multipliers forperforming a weighted multiplication by multiplying received signalsfrom said plurality of antenna elements by reception antenna weights,respectively; an adder for adding together the received signals of therespective antennas weighted by said plurality of first multipliers todeliver as single received data; a reception quality measuring circuitfor measuring a reception quality of the received data delivered fromsaid adder; reception antenna weight generating circuit applied with thereceived data delivered from said adder for generating weightingcoefficients which permit the received data to have an optimal value, assaid reception antenna weights; an antenna weight converting circuit forconverting the reception antenna weights generated by said receptionantenna weight generating circuit into transmission antenna weights; atransmission antenna weight control circuit that includes a memory thatstores (a) a set of fixed transmission antenna weights, (b) atransmission quality threshold, and (c) a most recent set of thetransmission antenna weights delivered from said antenna weightconverting circuit when the reception quality measured by said receptionquality measuring circuit exceeds the transmission quality thresholdstored in said memory, said transmission weight control circuitdelivering the transmission antenna weights delivered from said antennaweight converting circuit when the reception quality measure by saidreception quality measuring circuit exceeds the transmission qualitythreshold stored in said memory and delivering one of the fixedtransmission antenna weights and the most recent set of the transmissionantenna weights when the reception quality measured by said receptionquality measuring circuit is less than the transmission qualitythreshold stored in said memory; and a plurality of second multipliersfor multiplying data to be transmitted by the transmission antennaweight delivered from said transmission antenna weight control circuit,respectively.
 2. The adaptive antenna transmitting/receiving apparatusof claim 1, wherein said transmission weight control circuit deliversthe fixed transmission antenna weights when the reception qualitymeasured by said reception quality measuring circuit is less than thetransmission quality threshold stored in said memory.
 3. The adaptiveantenna transmitting/receiving apparatus of claim 1, wherein saidtransmission weight control circuit delivers the most recent set of thetransmission antenna weights when the reception quality measured by saidreception quality measuring circuit is less than the transmissionquality threshold stored in said memory.